The present invention relates to fluid displacement apparatus and more particularly to an improved scroll-type machine especially adapted for compressing gaseous fluids, and to a method of manufacture thereof.
A class of machines exists in the art generally known as "scroll" apparatus for the displacement of various types of fluids. Such apparatus may be configured as an expander, a displacement engine, a pump, a compressor, etc., and many features of the present invention are applicable to any one of these machines. For purposes of illustration, however, the disclosed embodiments are in the form of a hermetic refrigerant compressor.
Generally speaking, a scroll apparatus comprises two spiral scroll wraps of similar configuration each mounted on a separate end plate to define a scroll member. The two scroll members are interfitted together with one of the scroll wraps being rotationally displaced 180 degrees from the other. The apparatus operates by orbiting one scroll member (the "orbiting scroll") with respect to the other scroll member (the "fixed scroll" or "non-orbiting scroll") to make moving line contacts between the flanks of the respective wraps, defining moving isolated crescent-shaped pockets of fluid. The spirals are commonly formed as involutes of a circle, and ideally there is no relative rotation between the scroll members during operation, i.e., the motion is purely curvilinear translation (i.e. no rotation of any line in the body). The fluid pockets carry the fluid to be handled from a first zone in the scroll apparatus where a fluid inlet is provided, to a second zone in the apparatus where a fluid outlet is provided. The volume of a sealed pocket changes as it moves from the first zone to the second zone. At any one instant in time there will be at least one pair of sealed pockets, and when there are several pairs of sealed pockets at one time, each pair will have different volumes. In a compressor the second zone is at a higher pressure than the first zone and is physically located centrally in the apparatus, the first zone being located at the outer periphery of the apparatus.
Two types of contacts define the fluid pockets formed between the scroll members: axially extending tangential line contacts between the spiral faces or flanks of the wraps caused by radial forces ("flank sealing"), and area contacts caused by axial forces between the plane edge surfaces (the "tips") of each wrap and the opposite end plate ("tip sealing"). For high efficiency, good sealing must be achieved for both types of contacts, however, the present invention is primarily concerned with tip sealing.
The concept of a scroll-type apparatus has thus been known for some time and has been recognized as having distinct advantages. For example, scroll machines have high isentropic and volumetric efficiency, and hence are relatively small and lightweight for a given capacity. They are quieter and more vibration free than many compressors because they do not use large reciprocating parts (e.g. pistons, connecting rods, etc.), and because all fluid flow is in one direction with simultaneous compression in plural opposed pockets there are less pressure-created vibrations. Such machines also tend to have high reliability and durability because of the relatively few moving parts utilized, the relative low velocity of movement between the scrolls, and an inherent forgiveness to fluid contamination.
One of the difficult areas of design in a scroll-type machine concerns the technique used to achieve tip sealing under all operating conditions, and also speeds in a variable speed machine. Conventionally this has been accomplished by (1) using extremely accurate and very expensive machining techniques, (2) providing the wrap tips with spiral tip seals, which unfortunately are hard to assemble and often unreliable, or (3) applying an axial restoring force by axially biasing the orbiting scroll toward the non-orbiting scroll using compressed working fluid. The latter technique has some advantages but also presents problems; namely, in addition to providing a restoring force to balance the axial separating force, it is also necessary to balance the tipping movement on the scroll member due to pressure-generated radial forces, as well as the inertial loads resulting from its orbital motion, both of which are speed dependent. Thus, the axial balancing force must be relatively high, and will be optimal at only one speed.
One of the more important features of applicant's invention concerns the provision of a design for overcoming these problems. It resides in the discovery of a unique axially compliant suspension system for the non-orbiting scroll which fully balances all significant tipping movements. This permits pressure biasing of the non-orbiting scroll (which has no inertial load problems), the amount of such pressure biasing required being limited to the minimum amount necessary to deal solely with axial separating forces, thus significantly and beneficially reducing the amount of restoring force required. While pressure biasing of the non-orbiting scroll member has been broadly suggested in the art (see U.S. Pat. No. 3,874,827), such systems suffer the same disadvantages as those which bias the orbiting scroll member insofar as dealing with tipping movements is concerned. Furthermore, applicants' arrangement provides a control over non-axial movement of the non-orbiting scroll member which is greatly superior to that of prior art devices. Several different embodiments of applicants' invention are disclosed, using different suspension means and different sources of pressure.
One of the more popular approaches for preventing relative angular movement between the scrolls as they orbit with respect to one another resides in the use of an Oldham coupling operative between the orbiting scroll and a fixed portion of the apparatus. An Oldham coupling typically comprises a circular Oldham ring having two sets of keys, one set of keys slides in one direction on a surface of the orbiting scroll while the other set of keys slides at right angles thereto on a surface of the machine housing. The Oldham ring is generally disposed around the outside of the thrust bearing which supports the orbital scroll member with respect to the housing. Another feature of applicant's invention resides in the provision of an improved non-circular Oldham ring which permits the use of a larger thrust bearing, or a reduced diameter outer shell for a given size thrust bearing.
The machine of the present invention also embodies an improved directed suction baffle for a refrigerant compressor which prevents mixing of the suction gas with oil dispersed throughout the interior of the compressor shell, which functions as an oil separator to remove already entrained oil, and which prevents the transmission of motor heat to the suction gas, thereby significantly improving overall efficiency.
The machine of this invention also incorporates an improved lubrication system to insure that adequate lubricating oil is delivered to the driving connection between the crankshaft and orbiting scroll member.
Another feature of the present invention concerns the provision of a unique manufacturing technique, and wrap tip and end plate profile, which compensate for thermal growth near the center of the machine. This facilitates the use of relatively fast machining operations for fabrication and yields a compressor which will reach its maximum performance in a much shorter break-in time period than conventional scroll machines.